Pneumatic brake booster comprising improved sealing means

ABSTRACT

A pneumatic brake booster comprising an envelope ( 101 ) of longitudinal axis (Y) formed of a dish ( 105 ) having a rim ( 153 ) and a lid ( 103 ). The envelop ( 101 ) defining an interior volume ( 107 ) that is divided into a variable-pressure work chamber ( 109 ) and a low-pressure chamber ( 111 ) by a skirt ( 113 ). The skirt ( 113 ) is mounted to sealingly slide along the longitudinal axis (Y) of the envelope ( 107 ). The skirt ( 113 ) has a central orifice ( 115 ) with a pneumatic piston ( 117 ) sealingly mounted therein. A three-way valve ( 123 ) is mounted in the pneumatic piston ( 117 ) and is actuated by an actuating rod ( 125 ) connected to a brake pedal. The booster is characterized in that the sealing between the variable-pressure work chamber ( 109 ) and the low-pressure chamber ( 111 ) is achieved by a first sealing member ( 156 ) arranged between a radially internal first end of the skirt ( 113 ) and a radially external end of the piston ( 117 ) and a second sealing member ( 157 ) arranged at a radially external second end of the skirt ( 113 ) and an internal surface of the rim ( 153 ). The skirt ( 113 ) provides sealing between the radially external first end of the skirt and the radially internal second end of the skirt.

[0001] The present invention relates mainly to a pneumatic brake boostercomprising improved means of sealing between a variable-pressure firstpneumatic chamber and a second pneumatic chamber subjected to a lowpressure.

[0002] A pneumatic brake booster of the known type comprises an envelopedefining an interior volume divided by a skirt into a first workingchamber and a second vacuum chamber. The vacuum chamber is subjected toa low-pressure fluid, and the work chamber is a variable-pressurechamber the pressure being able to vary between a low pressure and ahigh pressure, for example air at atmospheric pressure. The skirt ofroughly annular shape receives, in its central part, a pneumatic pistonextending toward the rear of the booster and comprising a three-wayvalve. This three-way valve is actuated by an actuating rod connected toa brake pedal. Opposite the end of the three-way valve receiving theactuating rod is arranged a push rod which will actuate at least onepiston of the master cylinder. Sealing between the work chamber and thevacuum chamber is achieved between the skirt and the pneumatic pistonand between the skirt and the envelope by a single diaphragm, forexample made of rubber of roughly annular shape and fixed for example bytrapping to the exterior periphery of the pneumatic piston and also bytrapping to the interior periphery of the envelope between a first and asecond shell that form the envelope of the booster.

[0003] However, this type of sealing afforded by a diaphragm of roughlyannular shape poses problems in terms of cost. Indeed, there is asignificant materials cost because the diaphragm represents asignificant piece to be made with rubber, and there is also asignificant cost involved in manufacturing this diaphragm because it isof a relatively complicated shape, and finally, there is a high cost ofmounting in the booster because this mounting entails special tools anda certain amount of care in order not to damage this diaphragm. Inaddition, motor manufacturers are increasingly wanting to havelighter-weight products so as to lighten the vehicle, and this diaphragmbecause of its size makes a not insignificant contribution to the weightof the booster as a whole.

[0004] It is therefore an object of the present invention to offer aninexpensive means of sealing between the work chamber and the vacuumchamber.

[0005] Another object of the present invention is to offer a means ofsealing between the work chamber and the vacuum chamber that is simpleand economical to mount.

[0006] Another object of the present invention is to offer a means ofsealing between the work chamber and the vacuum chamber that is simpleto manufacture.

[0007] Another object of the present invention is to offer a means ofsealing between the work chamber and the vacuum chamber that is of lowweight.

[0008] These objects are achieved by a pneumatic brake boostercomprising an envelope split into a work chamber and a vacuum chamber bya skirt equipped in its central part with a pneumatic piston, sealingbetween the work chamber and the vacuum chamber at the contact betweenthe skirt and the pneumatic piston and the skirt and the internalperiphery of the envelope being afforded by two separate sealing means.

[0009] In other words, sealing between the piston and the skirt isperformed by means, for example, of an O-ring seal, and sealing betweenthe skirt and the internal periphery of the envelope is performed by asealing means sliding with sealing over the internal surface of theenvelope, and so the skirt in itself provides most of the sealingbetween the work chamber and the vacuum chamber.

[0010] The main subject of the invention is a pneumatic brake boostercomprising an envelope of longitudinal axis formed of a dish equippedwith a rim and a lid, said envelope defining an interior volume dividedsealingly into a variable-pressure work chamber and a low-pressurechamber by a skirt mounted to slide with sealing along the longitudinalaxis in the envelope, said skirt being equipped with a central orificein which a pneumatic piston is sealingly mounted a three-way valvemounted in the pneumatic piston and actuated by an actuating rodconnected to a brake pedal, characterized in that sealing between thevariable-pressure work chamber and the low-pressure chamber is achievedby a first sealing means arranged between a radially internal first endof the skirt and a radially external end of the piston and by a secondsealing means arranged at a radially external second end of the skirtand the internal surface of the rim, the skirt providing sealing betweenthe radially external first end of the skirt and the radially internalsecond end of the skirt.

[0011] Another subject of the invention is a pneumatic brake booster,characterized in that the first sealing means is an O-ring seal mountedin a groove made on the external periphery of the pneumatic piston.

[0012] Another subject of the invention is a pneumatic brake booster,characterized in that the second sealing means is a sealing piece oftubular shape fixed to the skirt and bearing against the interior faceof the rim of the dish and able to slide over said interior face.

[0013] Another subject of the invention is a pneumatic brake booster,characterized in that the sealing piece at a first longitudinal end isfixed by trapping in a fold made on an external radial end of the skirt.

[0014] Another subject of the invention is a pneumatic brake booster,characterized in that a low-pressure cavity is produced in the fold,between the interior end of the fold and the first end of the sealingpiece.

[0015] Another subject of the invention is a pneumatic brake booster,characterized in that the first end of the sealing piece has tabsoriented toward the actuating rod bearing, during braking, upon theskirt.

[0016] Another subject of the invention is a pneumatic brake booster,characterized in that a second longitudinal end of the sealing piece,forming a rearwardly-directed lip, is able to slide over the internalface of the rim of the dish.

[0017] Another subject of the invention is a pneumatic brake booster,characterized in that the sealing piece is made of rubber.

[0018] Another subject of the invention is a pneumatic brake boostercharacterized in that the sealing piece is made of slippery EPDM.

[0019] Another subject of the invention is a pneumatic brake booster,characterized in that the lid is fitted sealingly into the dish.

[0020] Another subject of the invention is a pneumatic brake booster,characterized in that the sealing element is an O-ring seal mounted in agroove formed in the external radial end of the lid and bearing againstthe internal face of the rim of the dish.

[0021] Another subject of the invention is a pneumatic brake booster,characterized in that the groove is produced by folding.

[0022] The advantage of the present invention is that it allows simpleadaptation to suit different types of booster with different envelopediameters simply by changing the size of the means of sealing betweenthe skirt and the internal surface of the envelope without having tomodify the shape of this sealing means.

[0023] The present invention will be better understood with the aid ofthe description which follows and of the appended drawings for whichfront and rear are, respectively, the left-hand part and the right-handpart of the drawings, and in which:

[0024]FIG. 1 is a view in longitudinal section of a booster of knowntype;

[0025]FIG. 2 is a view in section of a pneumatic brake booster accordingto the present invention;

[0026]FIG. 3 is a detailed view of FIG. 2.

[0027] In FIG. 1, the elements described hereinbelow are more or lesssymmetrical of revolution about the axis X, the longitudinal axis of thebrake booster described.

[0028]FIG. 1 shows a pneumatic brake booster of known type oflongitudinal axis X comprising an envelope 1 formed of a first and asecond shell 3 and 5, the shells 3 and 5 being crimped together aroundtheir exterior periphery. The shell 3 comprises a central orifice 4extending rearwards in the form of a hollow shaft 6 in which a pneumaticpiston 17 is sealingly slideably mounted, the shell 5 comprises acentral orifice 8 receiving a master cylinder 10. The envelope 1 definesan interior volume 7 divided sealingly into a work chamber 9 and avacuum chamber 11 by means of a skirt of roughly annular shape 13 ableto move along the axis X under a pressure difference. The skirt 13 inits central part comprises an orifice 15 in which there is sealinglymounted the pneumatic piston 17 comprising, at a first end directedforward, a part of roughly conical shape 19 with the vertex directedtoward the rear and, at a second end directed toward the rear a sleeve21. A three-way valve of known type 23 arranged inside the pneumaticpiston is operated by an actuating rod 25 connected to a brake pedal(not depicted). At rest, the three-way valve 23 places the vacuumchamber 11 and the work chamber 9 in communication, and during a brakingphase it places the work chamber 9 and the high-pressure externalenvironment in communication.

[0029] The braking action afforded by the driver and the boostingafforded by the booster is transmitted to at least one piston of themaster cylinder via a push rod 27. A reaction disk 31 is arrangedbetween a distributor plunger 29 forming part of the three-way valve 23and receiving a longitudinal front end of the control rod 25 and alongitudinal rear end of the push rod 27 and transmitting the reactionfrom the braking circuit to the brake pedal. A return spring 33 ismounted in compression in the vacuum chamber between the pneumaticpiston and the envelope allowing the pneumatic piston and the skirt toreturn to the rest position.

[0030] The vacuum chamber 11 is supplied with low-pressure pneumaticfluid via a sealed connector 35, the low-pressure pneumatic fluidcoming, for example, from the engine manifold depression or from apneumatic pump (not depicted).

[0031] Sealing between the front vacuum chamber 11 and the rear workchamber 9 is afforded by means of a diaphragm 39 in the form of a tube37 of a short length relative to its inside diameter and closed off atone end by an end wall 41, the diaphragm 39 providing sealing betweenthe skirt 13 and the envelope 1 and between the skirt 13 and thepneumatic piston 17.

[0032] The end wall 41 of the diaphragm 39, directed toward the rear,comprises a central orifice 43 receiving the front part 19 of the piston17 to which part the end wall 41 is fixed in a sealed manner by thetrapping of a bulge 45 bordering the periphery of the central orifice 43between the skirt 13 and the periphery of the piston 17. The diaphragm13 is also fixed sealingly inside the envelope 13 by the trapping of anannular bulge 47 bordering the front longitudinal end of the tubebetween the shells 3, 5.

[0033] The work chamber 9 is a variable-pressure chamber; at rest it isin communication with the vacuum chamber 11 and is therefore subjectedto the low pressure; during a braking action, the communication betweenthe vacuum chamber 11 and the work chamber 9 is interrupted and thecommunication between the work chamber 9 and the external environment isopened to allow a fluid pneumatically at high pressure to enter the workchamber 9, this high-pressure pneumatic fluid may, for example, be airat atmospheric pressure. The difference in pressure between the vacuumchamber 11 and the work chamber 9 causes the skirt 13 and the piston 17to move toward the push rod and therefore boosts the braking action ofthe driver on the brake pedal.

[0034] During braking and during the movement of the skirt along theaxis X and of the piston under the difference in pressure between thework chamber and the vacuum chamber, the diaphragm, commonly known as arolling seal, rolls along the radially internal wall of the envelope 1.

[0035]FIG. 2 shows a pneumatic brake booster according to the presentinvention.

[0036] In FIGS. 2 and 3, the elements described hereinbelow are roughlysymmetrical of revolution about the axis X, the longitudinal axis of thebrake boosters described.

[0037] The pneumatic brake booster according to the present invention,of axis Y, comprises an envelope 101, a skirt 113 mounted to slide withsealing in the envelope 101, a pneumatic piston 117 mounted fixedly in acentral part of the skirt 113, said piston 117 being equipped with athree-way valve able to place a low-pressure chamber 111, arranged infront of the skirt 113, in communication with a variable-pressurechamber 109 behind the skirt 113. Sealing between the chambers 111 and109 is performed by a first and a second sealing means 157, 156 whichare arranged respectively between the skirt and the envelope and betweenthe skirt and the piston.

[0038] The lid is formed of a lid 103 and of a dish 105 equipped with arim 153, for example made of thin pressed steel sheet, the lid 103fitting into the dish 105 and comprising a sealing means 159, forexample a seal, mounted fixedly in an annular groove 151 formed on theradially external periphery of the lid formed by bending the sheetmetal, the seal 149 being pressed sealingly against the internal surfaceof the rim 153 of the dish 105. The lid 103 comprises a central orifice104 extending rearward in the form of a hollow shaft 106 in which a rearpart of the pneumatic piston 117 is slideably sealingly mounted, and thedish 105 comprises a central orifice 108 receiving a master cylinder(not depicted). The envelope 101 defines an interior volume 107 in whichthere is slideably mounted with sealing along the axis Y, a skirt 113 ofroughly annular shape comprising, in its central part, an orifice 115 inwhich there is fixedly and sealingly mounted a forward-directed firstend 119 of the pneumatic piston 117 which end is formed of a firstsleeve force-fitted into the skirt 13. The orifice 115 is bordered by achannel 155 the exterior surface of which surrounds the sleeve 119 ofthe piston 117. The second first sealing means 156, for example anO-ring seal, is arranged in sealed contact against the exterior surfaceof the channel 155 in a groove 158 made on the exterior periphery of thesleeve 119 of the piston 117.

[0039] The vacuum chamber 111 being in communication with a vacuumsource, for example a vacuum pump or the engine manifold depression.

[0040] The sealing between the skirt 113 and the envelope 101 isperformed by the first sealing means 157 fixed with respect to the skirt113 and mounted so that it can move and able to slide along the interiorsurface of the rim 153 of the envelope 101.

[0041] The first sealing means 157 is formed of a portion of tube ofsmall length relative to its diameter, the diameter of the tube 157being roughly equal to the outside diameter of the skirt 113. A firstlongitudinal end 161 of the tube 157, directed forward, is mountedfixedly at a radially external end 163 of the skirt 113 by the trappingof this first end 161 of the tube 157 by means of an annular fold 165directed toward the actuating rod 125 and formed on the radiallyexternal end of the skirt 113. Advantageously, a low-pressure cavity 167is provided between the fold 165 and the first longitudinal end 161 ofthe part of the tube 157, and sealing tabs 169 on the exterior surfaceof the tube 157 trapped in the fold 165, said tabs 169 being directed inthe opposite direction to the low-pressure cavity 167.

[0042] During the braking phase, the tabs 169 are pressed hard againstthe skirt 113 because of the difference in pressure between the workchamber 109 and the low-pressure chamber 111, increasing the sealingbetween the skirt 113 and the tube 157.

[0043] At rest, the tabs 169 lift off the skirt 113 because thepressures in the vacuum chamber 111 and in the work chamber 109 becomebalanced, allowing the cavity 167 to be resupplied with low-pressurepneumatic fluid and thus making it possible to increase the sealingbetween the vacuum chamber 111 and the work chamber 109 in the brakingphase.

[0044] It is possible to anticipate the first end 161 of the tube 157being fixed sealingly to the skirt 113 in some way other than bytrapping, for example by attachment to the skirt; it will then benecessary to provide attachment means on the skirt and on the tube 157able to collaborate with each other, or by bonding, but there is then nolonger any need to provide the chamber at atmospheric pressure 172.

[0045] At a second longitudinal end 171 of the tube 157, directed towardthe rear, the external surface of the tube forms an annular lip 173 inroughly tangential contact with the internal surface of the rim 153 ofthe dish 105. The application of the lip 173 to the internal surface ofthe rim 153 of the dish 105 is increased during a braking phase by thedifference in pressures between the vacuum chamber 111 and the workchamber 109, the lip 173 actually being “sucked” toward the vacuumchamber 111 and becoming “stuck” to the internal surface 153 of the dish105. The lip 173 is long enough to provide the sealing of the twochambers 109, 111 without the risk of becoming situated between theradially external end of the skirt 113 and the rim 153.

[0046] The sealing depends on the force with which the annular seal 156is applied to the interior surface of the rim 153, which is, forexample, a force of compression of the annular seal between the skirtand the rim 153.

[0047] The sealing means 157 is made of an elastic material that issupple and airtight, for example of rubber or of slippery EPDM.

[0048] The pneumatic piston 117 is formed of a piece with approximatesymmetry of revolution, pierced with a longitudinal through-passage 179receiving a three-way valve 123 of known type actuated by an actuatingrod 123 connected to a brake pedal (not depicted), the valve 123 at restplacing the vacuum chamber 111 and the work chamber 109 in communicationand during a braking phase placing the work chamber 109 in communicationwith the high-pressure external environment.

[0049] We shall not describe the structure and operation of thethree-way valve, which are known.

[0050] The braking action supplied by the driver and the boostingsupplied by the booster is transmitted to at least one piston of amaster cylinder via a push rod 127. A reaction disk 131 is arrangedbetween a distributor plunger 133 forming part of the three-way valve123 and receiving a longitudinal front end of the control rod 125 and alongitudinal rear end of the push rod 127 and transmitting the reactionfrom the braking circuit to the brake pedal.

[0051] A return spring 133 is mounted in compression in the vacuumchamber, in the example depicted, it bears between a reinforcing piece179 applied against the internal surface of the dish 105 and the edgesof a roughly hat-shaped piece 177 the end wall of which collaborateswith the front face of the pneumatic piston 117 and the edges of whichare partially pressed against the front face of the skirt 113.

[0052] In operation, the driver depresses the brake pedal which movesthe actuating rod 125. There is therefore closure of the communicationbetween the vacuum chamber 105 and the work chamber 103 and opening ofthe communication between the work chamber 103 and the externalenvironment at atmospheric pressure. Because of the difference inpressure that arises between the work chamber 103 and the vacuum chamber105, the skirt 113 and the pneumatic piston 117 move toward the push rod127 along the axis Y. The outer end of the sealing means 157 able toslide sealingly, over the interior surface of the rim 153 of theenvelope 101 provides sealing between the work chamber 109 and the frontchamber 111 without impeding the longitudinal movement of the skirt inthe envelope 101.

[0053] There has indeed been produced a booster comprising means ofsealing between the vacuum chamber and the work chamber that are simpleand inexpensive because the sealing piece providing sealing between theinternal surface of the envelope and the skirt is manufactured from atube made of elastic and airtight material for example, of rubber orslippery EPDM, cut longitudinally to the desired length, and sealingbetween the skirt 113 and the pneumatic piston 117 is performed by meansof a standard O-ring seal of low cost price. It is therefore no longernecessary to produce a molded diaphragm in the form of a pot with bulgesbordering its ends.

[0054] In addition, mounting is simplified because the sealing means isfixed only to the skirt and simply rests against the internal surface ofthe envelope.

[0055] Of course a pneumatic brake booster comprising a work chamberarranged at the front of the booster and a vacuum chamber arranged atthe rear of the booster does not constitute a departure from the scopeof the present invention.

[0056] The present invention applies particularly to the motor industry.

[0057] The present invention applies mainly to the motor vehicle brakingindustry, particularly concerned with private cars.

We claim:
 1. Pneumatic brake booster comprising an envelope (101) oflongitudinal axis (Y) formed of a dish (105) equipped with a rim (153)and a lid (103), said envelope (101) defining an interior volume (107)divided sealingly into a variable-pressure work chamber (109) and alow-pressure chamber (111) by a skirt (113) mounted to slide withsealing alone the longitudinal axis (Y) in the envelope (107), saidskirt (113) being equipped with a central orifice (115) in which apneumatic piston (117) is sealingly mounted, a three-way valve (123)mounted in the pneumatic piston (117) and actuated by an actuating rod(125) connected to a brake pedal, the said sealing between thevariable-pressure work chamber (109) and the low-pressure chamber (111)is achieved by a first sealing means (156) arranged between a radiallyinternal first end of the skirt (113) and a radially external end of thepiston (117) and by a second sealing means (157) arranged at a radiallyexternal second end of the skirt and the internal surface of the rim(153), the skirt providing sealing between the radially external firstend of the skirt and the radially internal second end of the skirt, thesecond sealing means being a sealing piece (157) of tubular shape fixedto the skirt (113) and bearing against the interior face of the rim(153) of the dish (105) and able to slide over said interior face, thesaid sealing piece (157) at a first longitudinal end (161) is fixed bytrapping in a fold (165) made on an external radial end (163) of theskirt (113), characterized in that a low-pressure cavity (167) isproduced in the fold (165), between the interior end of the fold (165)and the first end of the sealing piece (157).
 2. The pneumatic brakebooster according to claim 1, characterized in that the first end (161)of the sealing piece (157) has tabs (169) oriented toward the actuatingrod (125) bearing, during braking, upon the skirt (113).
 3. Thepneumatic brake booster according to claim 1, characterized in that thefirst sealing means is an O-ring sal (156) mounted in a groove (158)made on the external periphery of the pneumatic piston (117).
 4. Thepneumatic brake booster according to claim 1, characterized in that asecond longitudinal end (171) of the sealing piece (157), forming arearwardly-directed lip (173), is able to slide over the internal faceof the rim (153) of the dish (105).
 5. The pneumatic brake boosteraccording to claim 1, characterized in that the sealing piece (157) ismade of rubber.
 6. The pneumatic brake booster according to claim 3,characterized in that the sliding piece (157) is made of slippery EPDM.7. The pneumatic brake booster according to claim 1, characterized inthat the lid (103) is fitted sealingly into the dish (105).
 8. Thepneumatic brake booster according to claim 7, characterized in that thesealing element (149) is an O-ring seal mounted in a groove (151) formedin the external radial end of the lid (103) and bearing against theinternal face of the rim (153 of dish (105).
 9. The pneumatic brakebooster according to claim 8, characterized in that the groove (151) isproduced by folding.